The present invention relates to a novel method for the conversion of sym-octahydrophenanthrene (sym-OHP) to sym-octahydroanthracene (sym-OHA) by a zeolite-catalyzed isomerization process.
Anthracene can be produced from sym-OHA. Anthracene and its derivatives such as anthraquinone have large volume uses in the dye industry as an important intermediate, in the chemical industry for making hydrogen peroxide, and in the pulp industry as a pulping agent. Low concentrations of anthracene can be found in coal tar.
Since phenanthrene may be viewed as an isomer of anthracene with respect to the ring-structure, much attention has been given to the conversion of phenanthrene to anthracene. Phenanthrene and its derivatives such as sym-OHP occur in high concentrations in coal-derived liquids, and can be obtained in relatively high yields from coal pyrolysis tars and carbonization tars. The isomerization of sym-OHP to sym-OHA is the key step in the conversion of phenanthrene to anthracene. A more detailed description of the applications of sym-OHA and anthracene are described in a recent publication in C. Song and H. H. Schobert, Fuel Processing Technology, 1993, vol. 34, No. 2, pp. 157-196.
Several U.S. patents have been granted to inventions on the isomerization of sym-OHP to sym-OHA using metal halides such as AlCl.sub.3 or AlBr.sub.3 (U.S. Pat. No. 4,367,360; 4,376,223; 4,376,224; 4,384,152; 4,384,156; 4,385,194). U.S. Pat. No. 4,376,223 to W. T. Gormley deals with the AlCl.sub.3 -catalyzed isomerization in the presence of an aryl phenone such as benzophenone, which serves as a promoter. Similarly, several other patents disclosed the same type of AlCl.sub.3 catalyzed or AlBr.sub.3 -catalyzed process but in the presence of an acyl peroxide such as benzoyl peroxide (U.S. Pat. No. 4,376,224 to W. T. Gormley), or in the presence of an aroyl halide such as benzoyl chloride or isophthaloyl chloride (U.S. Pat. No. 4,384,156 to W. T. Gormley), or in the presence of an aralkyl halide such as benzyl chloride (U.S. Pat. No. 4,385,194 to W. T. Gormley). U.S. Pat. No. 4,384,152 to K. Handrick et al. deals with the conversion of phenanthrene to anthracene in three steps: hydrogenation of phenanthrene to produce sym-OHP, isomerization of sym-OHP to sym-OHA using AlCl.sub.3 as catalyst, followed by dehydrogenation of sym-OHA to produce anthracene. Among the three steps, the isomerization of sym-OHP into sym-OHA is the most important step. In this invention, AlCl.sub.3 -catalyzed isomerization of sym-OHP to sym-OHA was carried out in the presence of methylene chloride solvent at a temperature from -30.degree. C. to +5.degree. C. U.S. Pat. No. 4,367,360 to W. T. Gormley deals with the isolation and recovery of AlCl.sub.3 catalyst (after the isomerization reaction of sym-OHP into sym-OHA) by using a liquid hydrocarbon solvent such as aliphatic solvent. Because of the highly hygroscopic, water-soluble, and environmentally harmful nature of AlCl.sub.3 and AlBr.sub.3, it is tedious to separate these metal halide catalysts from the products and to recover the catalysts.
The design of environmentally benign processes has become a significant focus of concern as the chemical industry seeks to alleviate the environmental impact of manufacturing processes. The present invention uses zeolites as catalysts for the isomerization of sym-OHP into sym-OHA. The process is more economical and environmentally benign, whereas metal halides such as AlCl.sub.3 or AlBr.sub.3 that are used in the previous inventions are environmentally harmful, corrosive, hard to handle and hard to recover. The advantages of the zeolite catalysts that can replace aluminum chloride (AlCl.sub.3) are numerous. The zeolites (aluminosilicate) catalysts can catalyze the reaction in place of toxic and corrosive compounds such as AlCl.sub.3 and AlBr.sub.3 and can be used in a much lower amount, e.g., less than 30 percent of the usual amount of AlCl.sub.3. Zeolites can be easily filtered off after the reaction and can be reused because they are not soluble in water or organic solvents. They are not chemical irritants and do not contaminate the products which makes them easy to handle and use.